A capacitance type sensor is used as a device for converting, into an electric signal, the intensity and direction of a force applied by an operator. For example, as an input device for a game machine used is a device incorporated as a capacitance type force sensor (so-called joy stick) for inputting operations in multidimensional directions.
Using the capacitance type sensor, an operation quantity with a predetermined dynamic range can be input as the intensity of a force applied by the operator. Such a sensor may be used in the form of a two-dimensional or three-dimensional force sensor capable of detecting each directional component divided from the applied force. In particular, a capacitance type sensor in which a capacitance element is made up of two electrodes and a force is detected on the basis of a change in the capacitance value due to a change in the interval between the electrodes, has a merit that a cost reduction can be intended by simplifying the construction. Therefore, sensors of this type have been put in practical use in various fields.
For example, Japanese Patent Application Laid-open No. 7(1995)-200164 discloses a capacitance type force sensor as illustrated in FIG. 36. The force sensor 510 is made up of a substrate 520, an elastic rubber sheet 530 provided on the substrate 520, an electrode 540 provided on the lower face of the elastic rubber sheet 530, electrodes 500 to 504 (see FIG. 37) provided on the upper face of the substrate 520, a holder plate 560 for supporting and fixing the elastic rubber sheet 530 to the substrate 520, and an electronic device 580 provided on the lower face of the substrate 520. As illustrated in FIG. 37, the electrodes 500 to 504 are constituted by four electrodes 501 to 504 disposed symmetrically around the origin, and an annular electrode 500 disposed outside them. An outer peripheral portion of the electrode 540 is in contact with the electrode 500, which is grounded, so that the electrode 540 is also grounded through the electrode 500.
When an operator depresses the elastic rubber sheet 530, the elastic rubber sheet 530 is deformed downward to change the respective distances between it and the four electrodes 501 to 504. The capacitance values of the respective capacitance elements formed between the four electrodes 501 to 504 and the electrode 540 change accordingly. Thus, by detecting the changes in the capacitance values, the intensity and direction of the force applied by the operator can be known.
On the other hand, Japanese Patent No. 3020736 discloses a capacitance type acceleration sensor as illustrated in FIG. 38. The acceleration sensor 610 is made up of a fixed substrate 620, a flexible substrate 621, a fixed electrode 600 provided on the fixed substrate 620, displacement electrodes 641 to 645 (see FIG. 39) provided on the flexible substrate 621, an action member 630, and a device casing 660. As illustrated in FIG. 39, the displacement electrodes 641 to 645 are constituted by four electrodes 641 to 644 disposed symmetrically around the Z-axis, and a disk-shaped electrode 645 disposed inside them. The fixed electrode 600 is grounded through a not-illustrated wire.
When a force is applied to an application point P, the flexible substrate 621 is curved. The displacement electrodes 641 to 645 thereby move upward to change the respective intervals between them and the fixed electrode 600. The capacitance values of the respective capacitance elements formed between the five displacement electrodes 641 to 645 and the fixed electrode 600 change accordingly. Thus, by detecting the changes in the capacitance values, the intensity and direction of the force applied to the application point P can be known.
As described above, in case of the force sensor 510 illustrated in FIG. 36, the electrode 540 is grounded through its outer peripheral portion being in contact with the electrode 500. Therefore, the force sensor 510 has no need of a wire for grounding the electrode 540. In this force sensor 510, however, since the electrode 540 is electrically connected directly to the electrode 500, if a high voltage is applied to the electrode 540, a spike current may flow in the substrate 520 that is supporting the electrode 500. There is a possibility of a trouble with or a breakdown of the force sensor 510. That is, the force sensor 510 is inferior in view of its withstand voltage characteristic. Besides, if the electrical connection between the electrodes 540 and 500 has become bad due to aged deterioration or the like, an accurate sensor output cannot be obtained. Thus, the force sensor 510 illustrated in FIG. 36 is unsatisfactory in view of its reliability.
On the other hand, the acceleration sensor 610 illustrated in FIG. 38 is superior in view of its reliability. But, since the capacitance elements are in parallel relation in a way, the fixed substrate 620 must be provided with a wire for grounding the fixed electrode 600, besides the flexible substrate 621 supporting the displacement electrodes 641 to 645 must be provided with wires for supplying external signals to those electrodes. However, providing both of the fixed and flexible substrates 620 and 621 with such wires brings about a complicated structure and a complicated manufacturing process of this kind of acceleration sensor.
A primary object of the present invention is to provide capacitance type sensors high in reliability and simple in manufacturing process and structure.